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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 8: Poster Session SYOE
SYOE 8.43: Poster
Dienstag, 27. März 2007, 18:00–20:00, Poster B
Interplay of chain geometry and quantum coherence in a conjugated polymer — •E. Da Como1, K. Becker1, J. M. Lupton2, and J. Feldmann1 — 1Photonics and Optoelectronics Group, LMU, Munich, Germany — 2University of Utah, Salt Lake City, USA
The performance of optoelectronic devices based on conjugated polymers depends on the influence of morphology on the electronic structure. Within this context, we correlate the photophysics and the chain morphology of a model fluorene polymer, poly-(9,9-dioctylfluorene) (PFO), at the single molecule level. PFO shows different phases that can be identified by photoluminescence spectroscopy. Well resolved and red-shifted emission bands are observed for the planarized beta-phase while a less structured blue emission is characteristic of the glassy phase. The identification of these features, at the single molecule level [1], raises the question of how chain geometry influences the electronic properties. Using low temperature single molecule excitation polarization anisotropy measurements we probe the conformation of isolated chains in both phases. The results demonstrate that beta-phase molecules show higher polarization values than the twisted glassy phase molecules, reflecting an elongated character of these chains. Most importantly, a strong correlation exists between the zero phonon linewidth and the emission polarisation anisotropy of the beta-phase molecules. Extremely narrow lines (0.5 meV) are observed for fully polarized emission. This indicates that the beta phase constitutes a 1D crystalline polymer where the exciton can reach quantum coherence times of ~3 ps. [1] K. Becker et al. JACS, 127, 7306 (2005).